1. Technical Field
The invention relates in general to a charge pump and a phase detection apparatus, a phase-locked loop and a delay-locked loop using the same.
2. Background
In the increasingly precise chip application field nowadays, system-on chip (SoC) is an inevitable trend. However, internal circuits of the chip need a clean and steady clock generator to provide clock signals of the system. Therefore, a phase-locked loop (PLL) or a delay-locked loop (DLL) is widely applied to the clock generator of the system for generating low jitter clock signals that free from affected by manufacturing procedures. In the architecture of the PLL and DLL, a charge pump PLL and a charge pump DLL are architectures the field uses most often due to the simple implementation and easy production.
Because the charge pump is important in the analog block, the circuit design of the charge pump occupies high importance in the circuit architecture of the charge pump PLL and the charge pump PLL. The circuit design of the charge pump greatly affects performance of the PLL and the DLL. Hence, how to more improve efficiency, accuracy and speed of the charge pump circuit is an important issue in the design of the locked loop.
Referring to FIG. 1, a schematic illustration of an example of a traditional charge pump is shown. Take a charge pump 10 to be applied in a phase-locked loop to be exemplified, and it is not limited thereto. In the phase-locked loop, the charging/discharging timings are decided according to the switches SW1 to SW4 and SWR, and a reset operation is performed at an end of each reference period. If the charge current is not matched with the discharged current, the phase-locked loop will adjust the charging/discharging time to achieve charge equivalent and keeps locked. However, the charge pump 10 suffers from the problem of the unmatched currents and causes higher ripples as being locked. That is, there are spurs occurred in the frequency spectrum. When high frequency clock signals generated by the phase-locked loop have components of spurs and interference signals are just located on the same frequency offset, a frequency modulation may be caused and then the SNR of the signal is lowered.
Referring to FIG. 2, a schematic illustration of another example of a traditional charge pump is shown. To solve the problem of the unmatched currents, a charge pump 20 in FIG. 2 applies an operational amplifier OPA to force the charge current and the discharge current to be equal. However, the above-mentioned method may consume larger areas in the circuit architecture, and may further cause the charge pump 20 and application circuits thereof to be limited to a frequency bandwidth or a gain of the operational amplifier OPA.